It is well known to the experts in the art of power lines construction that the stringing and clamping-in procedures usually comprise the following operations:
position one pulley per each crossarm of each tower and suspend each of said pulleys from the strings of insulators hanging from each crossarm,
lay on the ground one service cable per each phase of the power line according to the layout of the towers,
lift and position each service cable on each respective pulley,
tension each of said service cables from one end by means of a winch and from the other end by means of a brake,
pull the service cables by means of said winch, and replace each service cable with a conductor and/or a larger draw cable if a bundle of conductors has to be positioned per each phase of the line,
position all conductors and/or bundles of conductors on their respective pulleys, while keeping said conductors and/or bundles of conductors always under tension and therefore always raised from the ground,
pull the conductors and/or bundles of conductors by means of said winch till they reach the prescribed degree of tension (pre-sagging) (if longitudinal unbalances are present the pre-sagging of the conductors at this stage cannot be the equal to the final and correct sagging),
if longitudinal unbalances are present, due to the fact that the power line is crossing mountains and/or the distance between towers is not constant, calculate said longitudinal unbalances, and mark the plumb-point on each conductor so that once the conductors have been clamped-in to said insulators, the insulators will be plumbed and the conductors sagged,
temporarily lift, by means of one or more tackles, the conductor and/or each conductor of a bundle from the grooves of a pulley, remove said pulley, clamp-in the conductor and/or conductors to the insulators, and once all conductors have been clamped-in to the insulators of all towers between the brake and the winch, control, and often adjust, the sagging of said conductors.
It is to be understood that when longitudinal unbalances are present, before the crews can proceed with the last described operation, that is to say before they can clamp-in the conductors, said tackles have to be used not only to lift the conductors from the pulleys, but also to pull said conductors, with repeated operations, in order to recover the calculated differences between the "rest" position of the conductors on the pulley and the final clamp-in points. This additional operation has to be carried out with absolute accuracy so that once said conductors have been clamped-in to the insulators of all towers between the brake and the winch, said insulators will remain perfectly plumbed, and only vertical loads will be imposed to the crossarms of suspension towers.
There are many difficulties related to the stringing of power lines and while some of them, particularly these relating to the positioning of the service cables on the towers, have been faced and solved for example as described in the U.S. Pat. No. 4,596,379 (Europe N.56285) of the same assignee, patent that can be referred to for a better understanding of state of the art of the different stringing methodologies, the others, and particularly those relating to the clamping-in and plumbing operations, have been faced, but not solved.
The difficulties relating to the clamping-in of the conductors to the insulators, as partially explained, are the following:
1. stringing conductors on angle towers, that is to say on towers which cause the conductors to run on different vertical planes, causes the pulleys to be displaced to a non-vertical position. The displacement of the pulleys, in its turn, causes the conductors to cross the grooves of the pulley. In fact, while the two catenaries adjacent to the tower are points. This additional operation has to be carried out with absolute accuracy so that once said conductors have been clamped-in to the insulators of all towers between the brake and the winch, said insulators will remain perfectly plumbed, and only vertical loads will be imposed to the crossarms of suspension towers.
There are many difficulties related to the stringing of power lines and while some of them, particularly those relating to the positioning of the service cables on the towers, have been faced and solved for example as described in the U.S. Pat. No. 4,596,379 (Europe N.56285) of the same assignee (that patent that can be referred to for a better understanding of state of the art of the different stringing methods), the problems relating to the clamping-in of the conductors to the clamps of the insulator chain, while keeping the conductors always under tension have been faced, but not solved.
The difficulties relating to the clamping-in of the conductors to the insulators, as partially explained, are the following:
1. stringing conductors on angle towers, that is to say on towers which cause the conductors to run on different vertical planes, causes the pulleys to be displaced to a non-vertical position. The displacement of the pulleys, in its turn, causes the conductors to cross the grooves of the pulley. In fact, while the two catenaries adjacent to the tower are contained on perfectly vertical planes, the plane on which the pulley sheaves rotate is (in these cases) always sloped. Consequently, the conductors simultaneously touch the grooves of the pulley in points with different peripheral speeds undergoing continuous abrasions and torsions which should not be allowed in order to preserve their integrity. PA0 2. When longitudinal unbalances are not present, the points where the conductors rest in the grooves of the pulleys coincide with the points where the suspension clamps have to be inserted for clamping-in. Consequently, said points of the conductors cannot be accessed by the crews for clamping-in without first having to temporarily lift said conductors and remove the pulleys. PA0 3. When longitudinal unbalances are present, the clamping-in points do not coincide with the points where the conductors rest in the grooves of said pulleys, but on the contrary they often are various meters away from said rest-points. In these cases, the final sagging, clamping-in, and plumbing operations always require the processing of complicated calculations and the execution of difficult operations to be carried out exclusively on the towers in order to: PA0 4. The sagging, plumbing, and clamping-in operations briefly described in point 3, can get to be so complicated that in the end, many times, they turn out to be mostly trial and error operations. Many times, after the conductors have been clamped-in to all towers, said conductors will still be not perfectly sagged. In these cases the crews will have to go back from tower to tower and adjust the clamp-in points till said conductors will be perfectly sagged and all insulators perfectly plumbed.
recover said longitudinal unbalances on line towers, PA1 recover said longitudinal unbalances even on angle towers while for example also compensating for the different lengths of the conductors in a bundle, and PA1 clamp-in the conductors according to a specific geometric configuration. In addition to the complicated operations required to undo said longitudinal balances, these cases too always require to first temporarily lift the conductors from the pulleys, using numerous and supplementary pieces of equipment, and then remove the pulleys before clamping-in.
In the Italian patent N.1191291, of the same assigned, the problems and difficulties listed in points 1 and 2 had been dealt with through the use of common pulley sheaves which had been mounted specularly on a special frame. Even though said pulley-units in theory partially solved some of the mentioned inconveniences and difficulties, they required the use of many pulley sheaves having diameter at least equal to 80 cm.. The number of pulley sheaves required was more than double the number of conductors in a bundle, in fact for example in the described case of a bundle of eight conductors the pulley-unit was composed by twenty pulley sheaves, sixteen of which had diameter equal to 80 cm.. The number of pulley sheaves, their diameter, and the heavy structure of the frame added up to an enormous increase of the weight, size, and manufacturing costs of the whole unit. In addition, the weight and size of the unit also created considerable difficulties to transport it to the towers and suspend it from the insulators. Because of these reasons and other technical problems, the use of the pulley units described was completely inefficient, uneconomic, and unjustifiable.
The present invention offers the best and most practical solution to the difficulties listed in points from 1 to 4 and the technical and operative/economic problems related to the pulley-units described in the Italian patent N.1191291. The present invention relates to: 1) the general stringing method, because the clamping-in and sagging operations have been substantially changed and; 2) the structure of the suspension devices that allow to string the service cables and/or conductors.
The new structure of the suspension devices, according to the present invention, allows: 1) the conductors and/or cables to freely run on said devices while stringing, 2) the insulators to be automatically and perfectly plumbed and the conductors to be automatically and perfectly sagged without the need of manual interventions and/or counterweights, and 3) the conductors to be directly clamped-in without the need of either lifting said conductors from their rest-position or using temporary and supplementary equipment. All being accomplished while at the same time decreasing both the size and the weight of the suspension units. It is also to be noticed that the structure of the suspension units, according to the present invention, also allows to position all clamps necessary for the clamping-in operations within each suspension unit further decreasing work time, and further simplifing the job to be carried out by the crews.
It is well known, that pulleys and/or pulley units commonly used generally comprise: 1) a large suspension frame, to be suspended from the insulators often in correspondence of at least one of the holes designed for receiving the suspension clamps, in other words often occupying at least one of the clamp-in points, and 2) one or more pulley sheaves.
The diameter of these pulley sheaves is usually very large, greater for example than 60 cm. and often even greater than 100 cm.. in order to allow the conductors to run on said sheaves without bending too much. Because of the present trend of using conductors with larger diameters, the pulley sheaves are also tending to have larger diameters.
The just mentioned facts together with the tendency of using one bundle of conductors per each phase of the line, rather than one single conductor, are the reasons why the commonly used pulleys have become larger and heavier. In fact, the commonly used pulleys, for example for a bundle of three conductors, weigh approximately 150-200 Kg., while the pulley unit for a bundle of eight conductors, described in the Italian patent N.1191291, weighs approximately 1,500 Kg., and/or about 500 Kg. in the not described case of a unit for three conductors. The weight of the commonly used pulleys and/or pulley units described in said patent is not only an inconvenience from the manufacturing/cost point of view, but more than anything else from the point of view of their practical use on site. The pulleys and/or pulley units have to be transported along the power line, often in areas which cannot be reached by road and/or cross country vehicles, lifted and suspended from the insulators for stringing, and finally transported again to another tower. It is quite obvious that when a pulley and/or pulley unit weighs more than 150-200 Kg. and/or more than 500-1,500 Kg. the transportation and lifting problems can become particularly burdensome.
As mentioned earlier, another serious problem related to the use of the common pulleys derives from the difficulty of clamping-in the conductors, both because of the reasons explained in points from 1 to 4, and because of the fact that often at least one of the clamp-in points has been occupied by the frame of the pulley. If using the common pulleys for stringing is therefore necessary to first remove said pulleys from their suspension point and then clamp-in the conductors. For these operations, to be repeated for each pulley of each tower, the procedure is usually the following: first, temporarily lift the conductor and/or conductors, by means of one or more tackles and bring said conductor and/ or bundle of conductors in position to be clamped-in, secondly remove the pulley and bring it to the ground, and finally clamp-in the conductor and/or bundle of conductors to the insulators at the "right" points. These are very complicated operations particularly in consideration of the fact that the weight of each conductor to be temporarily lifted can easily be greater than 1,000 Kg. and/or greater than 2,000 Kg.. As mentioned earlier, it is important to understand that when longitudinal unbalances are present the final clamp-in points of each conductor never correspond with the rest-points of said conductors on the pulleys, but can get to be even more than 10 m. away (down-hill) from said rest-points. In these cases the tackles that are applied on each conductor to lift them from the grooves of the pulleys, have to be attached to each conductor down-hill and far away from the pulleys, in order to recover said various meters of conductors that cause the insulators to be out-of-plumb. This complicated operation also implies to impose a longitudinal stress of thousands of kilograms to each crossarm of many suspension towers, which are neither designed nor manufactured to resist to said longitudinal stress, but only to vertical loads.
Suspension system of the type comprising a small frame and a plurality of rollers disposed in continuous sequence as one sector of a crown, have been described in the U.S. Pat. No. 3,145,016 and in the French patents N.93165 and N.1104834. The primary objects of these patents were: 1) for U.S. Pat. No. 3,145,016 to allow a sector of multiple pulley assemblage to automatically change the angle of load imposed on the conductors in order not to damage said conductors while stringing, 2) for the French patent N. 1104834 to reduce the weight and size of the suspension units and 3) for the French patent N. 931675 to be able to use the same suspension unit for stringing any size conductors manually changing the position of the wheels so as to vary the angle of loads imposed on different conductors. On the other hand, none of these devices was technically fitted to be practically used on site.
In addition, none of the listed patents allowed to either clamp-in the conductors directly (and at the right point) to the insulators without first having to remove the suspension units, or to string the conductors passing through transversal angles without damaging the conductors. Moreover, none of the listed patents allowed to, automatically plumb the insulators and perfectly sag the conductors, and automatically position a bundle of conductors according to the prescribed geometric configuration, neither simultaneously on all towers between the brake and the winch, nor with one or more operations without a direct intervention of the crews on the conductors themselves.